<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <select name="" id="sle1" onchange="onc()">
        <option value="">请选择正确的网站</option>
        <option value="http://www.baidu.com">百度</option>
        <option value="http://www.bilibili.com">B站</option>
        <option value="http://www.taobao.com">淘宝</option>
    </select>
</body>
    <script>
        function onc(){
            var url=document.getElementById('sle1').value;
            location.href=url;
        }
    </script>
</html>